1. Field of the Invention
This invention relates to an apparatus and method for cooling refractory sand used in the making of foundry molds and, more particularly, relates to cooling refractory sand used in no-bake molding.
2. Description of the Prior Art
Casting is one of the most common and economical metal forming techniques and involves the pouring of molten metal into a preformed cavity in a mold, wherein the metal then solidifies. The mold can be made from sand or other molding material. After solidification, a cast metal shape is removed from the mold by knocking away the outer molding material. This molding material is then reused to form new molds.
Refractory sand is the main component in making common foundry molds. The sand is constantly recycled from used, hot molds and returned to a storage bin. As a result of this constant recycling, the temperature of the sand in the storage bin is typically elevated above ambient temperature.
At present, there are two common methods of forming a sand based foundry mold. In a first method, called "green sand molding", a binding material composed of clay, water and other additives is mixed with the refractory sand to form a free flowing, homogeneous mixture. A mold cavity is formed by pouring this mixture over a pattern which is then removed to form the cavity.
In a second common method, called "no-bake molding", sand is supplied to a mixing device. A resin binder is then added to the sand. A catalyst is added to promote curing of the binder. This mixture is then poured over a mold forming pattern and allowed to harden prior to use.
The resin binder is very temperature sensitive. If sand is supplied to the mixing device at too high a temperature, the binder begins to cure in the mixing device, thereby prematurely hardening the mixture. Thus, by the time the mixture is supplied to a molding station, it has already bonded to such an extent that it is too stiff to be used in the mold.
To prevent this premature curing of the resin binder caused by elevated refractory sand temperatures, various sand cooling methods have been developed. In U.S. Pat. No. 4,304,286 to Waldron, a liquefied gas is injected into a conduit through which the sand is falling to reduce the sand temperature below the resin curing temperature. Other cooling methods include the use of fluidized beds and water sprinkling systems.
The main purpose of the prior art cooling methods is to control the refractory sand temperature primarily to prevent premature curing of the resin binder. The effect of the moisture content in the refractory sand on the binder has not heretofore been a consideration in the prior art.
Moisture sensitive binders have been developed for which temperature control alone is insufficient. Thus, the problem of moisture accumulation in the sand is also an important concern since accumulated moisture reacts with the moisture sensitive binder to affect premature binder curing.
Accordingly, it is an object of the instant invention to overcome the deficiencies in the prior art with respect to cooling refractory sand and to controlling moisture content thereof.